Cobalt solution purification



July w, N490 R. E. cHURcHwARD ET AL 2,476,284-

COBALT SGLUIION PURIFICATION Filed Jan. 1, 1945 z.. "-eg -Z 6 f [5 Zig/351 Z5' l" Patented July 19, 1949 COBALT SOLUTION PURVIFIOATION Ruth E. Churchward and Francis K. Shelton, v v Boulder City, Nev.

' Application January 1, 1945, Serial No. 570,936

(Granted under the act of March 3,1883, as amended April 30, 1928; 370 0. G. 757)' Z Claims.

The invention described herein may be manufactured and used by or for the GovernmentY of the United States for governmental purposes without the payment to us of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to the production of purified cobalt compounds, and more particularly to the production of a cobalt compound of sufcient purity to be suitable for metallic cobalt electrowinning purposes.

In the production of metallic cobalt by electrolysis from a suitable solution, such as for exfainple one containing cobalt sulfate, boric acid and sodium fluoride, it is important to remove as completely as possible any impurities interfering with the rapid and smooth plating out of the cobalt metal. Certain harmful impurities occur in relatively large amounts in cobalt solutions preparecl by usual methods, suitably by extracting cobalt ore concentrates with acids. Among such impurities are zinc, copper, iron, cadmium, mercury, arsenic, and antimony. Other harmful impurities which are present or may occasionally be present are gallium, thallium, bismuth, palladium, ruthenium, osmium and indium. These latter substances may be present in such small amounts as to defy chemical detection, but nevertheless interfere with a satisfactory cobalt electrodeposition.

It is accordingly an object of this invention to prepare a purified cobalt compound suitable for metallic cobalt electrowinning purposes and a further object is the purification of contaminated cobalt electrolytes. Many other objects and advantages will be apparent or will appear hereinafter as the ensuing description proceeds.

The foregoing and other objects are accomplished in accordance with this invention wherein Y acid such as for example a strong mineral acid` which may include nitric acid, hydrochloric acid and preferably sulfuric acid. For illustrative nection with the purification of a cobalt sulfate solution but it is not to, be limited thereto.

Suitable soluble suldes for employment in accordance with this invention include the soluble suldes and polysuldes of the alkali lmetals and ammonia, examples being ammonium sulfide, p0- tassium sulfide, and sodium sulfide. Preferably, for reasons of economy, convenience and purity of the resulting cobalt compound, hydrogen sulfide is employed as a soluble sulfide precipitating reagent- Y Desirably, hydrogen sulde is employed under an elevated superatmospheric pressure of at least ten pounds per square inch gauge, suitably between 15 and 100 pounds per square inch gauge. In general we have found a pressure of about 20 pounds per square inch gauge to be entirely satisfactory and preferable. However, the upper limit of pressure under which our sulde treatment is carried out is limited only by the strength of the reaction equipment.

The treatmentof the cobalt sulfate or other soluble cobalt salt in solution with a soluble sulde is carried out under acidic solution conditions, an'd generally the solution is maintained within an acidity rangeA between about pI-I 1 and pH 6,-,and preferably the acidity is maintained within the more restricted range of between about pH 4 and pH 5. The pH or solution acidity mayv be brought and maintained within the desired range by any of the customary means known to those skilled inthe art, but ordinarily we prefer to incorporate cobalt oxide or carbonate to elevate the solution pH when necessary, and an innocuous mineral acid such as for example boric acid, sulfuric acid or hydrochloric acid, can be employed to lower the solutionpH.

Suitable apparatus for carrying out'the precipitation treatment of this invention is illustrated in the accompanying drawings in which:

Figure 1 illustrates in diagrammatic form a suitable arrangement of apparatus.

Figure 2 illustrates in diagrammatic form a somewhat simpler alternative arrangement of suitable apparatus for carrying out this invention.

In operation, and referring now to the drawings, cobalt solution to be treated is stored in a suitable .container II and a soluble sulfide, for example hydrogen sulfide is stored in another suitable vessel I4. Cobalt solution from the container II passes by Way of a pump 20 through a pair of inlet valves 22 and I9y into a pair of reaction vessels I2 and I3. During introduction of the cobalt solution, a pressure relief valve I1V purposes, the invention will be desllbetl 9011-. Ill iS maintain@ th? .09911 Position The $919311? solution is allowed to enter the reaction vessels I2 and I3 until the liquid level indicator I6 shown as a sight glass indicates a suitable quantity of cobalt solution has been admitted. Thereupon, the pump and the inlet valves 22 and I9, are closed and the pressure relief valve `I1 is likewise closed. Hydrogen sulfide or other soluble sulfide is admitted to the reaction vessels I2 and I3, which are interconnected at their upper portions by a pipe 28 and through their lower portions by a pipe system including a valve 23, a secondA pump provided with a priming device 21 and a second valve 24. After admission of hydrogen sulfide from the storage vessel I4 through inlet valve 3| and a suitable pipe 30, the "pressure upon 'the reaction chambers I2 and I3 is elevated to a. predetermined value as indicated on a suitable gauge I5 which may be 20 pounds per square inch guage. Thereupon, the valves 2'3 and 2:4 are opened, the circulating pump 25 is started, and the solution in the -reaction 'chambers proceeds from one chamber vI3 through pump 25 and the second chamber I2 and thence back to chamber I3 by way of circulating leg 28 which is optionally provided with 'a spray head 29 in chamber I3.

The circulation is continued until a desired degree of saturation is obtained, then thereupon the sulfide inlet valve 3l is closed, the circulating pump 25 is stopped, the vent valve I1 is opened to release excess pressure y'and the discharge valve 2l is opened thus draining the reaction chambers I2 and I3 into a 4storage and 4settling tank I8. The purified solution can beseparated from the formed precipitate by decantation, filtration and the like in suitable apparatus not shown. Thereupon, the purified cobalt compound can be recovered from the purified solution, if desired, by crystallization, evaporation and the like. Desirably, purified solution has incorporated therein about 50 grams per liter of boric acid-and 5 grams per liter of sodium fluoride to form a suitable fluoborate electrolyte for cobalt electrowinning.

An alternative arrangement of suitable apparatus as shownin Figure V2 comprises an elevated storage vessel 38 communicating With a lower reaction vessel 40 by Way of pump 5I, a regulating valve 50 and a pipe 49. The lower reaction vessel 40 is connected to the upper container 48 by means, of the elevated pipe system 42 and 44 designed to place the pipe section 44 under a suitably elevated pressure for carrying out the treatment. Hydrogen sullide or other soluble sulfide is admitted to the system from a suitable storage container 46 by Way of an inlet valve 41 and a pump 4I which serves both to circulate the treatment liquors and to create a suitable pressure in the pipe section 44 in conjunction With the regulating valve 45. The pressure existing in the pipe section 44 is dependent upon the vertical height thereof as well as with pressure created by the pump 4I and maintained by the regulating valve 45. In operation, the pumps 4I and 5I are started, hydrogen sulfide is admitted to the system and the solution undergoing treatment proceeds from storage vessel 48 through the pump 5I and the pipe 49 into a reaction vessel 40 and thence through low pressure pipe 42 into thehigh pressure pipe 44 where it is treated'with hydrogen sulde admitted through the pump 4I. The solution then passes through regulating valve and into storage chamber 48 again. After a suitable length of treatment,the pumps may be stopped, and the treated solution allowed to settle in container 48 from which purified cobalt solution canlbe decanted by means-not shown.

VIIi

In addition to the simple treatment of the soluble cobalt compound under acidic conditions with a soluble sulfide as described above, we have found it highly desirable to carry out the sulde treatment in the presence of a precipitate-forming amount of a normally soluble salt of a heavy metal from the group of copper and iron, then treating the resulting mixture with an innocuous voxidizing agent, and separating a purified cobalt 10 solution from the impurity-containing residue. Desirably, this precipitation treatment can be carried ,out by dissolving an excess of a soluble .copper compound and a soluble iron compound in a cobalt solution to be purified, then precipitating from said solution an insoluble copper compound together with impurities, and thereafter an insoluble iron compound together with further impurities. We have found that the precipitation of an insoluble copper compound from solution carries With it not only the undesired copper sulfide but also a -greatrnany impurities which cannot be determined chemically but which detrimentally affect thesubsequent electrolysis of the cobalt solution and tend to yield a poor metallic cobalt deposit. Desirably, the previously sulfide treatment is carried out in the presence of at least .1 gram .of va normally soluble copper compound per liter of solution and usually the sulde treatment should be carried out in the presence of between .l and `10 grams of a normally soluble copper compound per liter of solution. rIhe copper compound can be added in the form of any of thev normally soluble compounds of copper such as for example copper nitrate, copper formate, copper acetate, copper chloride, and preferably copper sulfate.

vIt has also beenfound, that the precipitation of an iron compound from solution also carries with it a .great number of impurities which detrimentallyaffect 'subsequent electrolysis of the cobalt solution. The exact nature of the impurities cannot definitely be determined, but electrolysis of a cobalt solution before and after treatment in accordance with .the iron precipitation step about 45 to be described establishes beyond question the eiiicacy'of our iron precipitation treatment. In carrying out this precipitation we treat the solution, either before or 'after the sulde treatment, With an excess of an innocuous oxidizing 50 agent in the presence of at least .1 gram of dissolved iron per liter of cobalt solution undergoing treatment. Generally, it has been found that between about .1 and 10 grams of dissolved iron per liter of solution Vforms ra suitable amount of dissolved iron for precipitation. The dissolved iron is preferably precipitated by treatment at an acidity notmore acid than pH 3.2 and at elevated solution temperature of at least about 50 to 60 degrees centigrade. The cobalt solution containing a suitable quantity of dissolved iron is treated by passing atmospheric air into and through the solution until -.substantially all lof thev dissolved iron is precipitated in the form of occulent ferrie hydroxide. Other suitable oxidizing agents can be employedinstead of atmospheric air, examples being hydrogen peroxide, sodium perborate and similar oxidizing agents which do not detrimentally affectsub'sequent electrolysis of the solution. Atmospheric air is cheap and convenient and constitutes a preferred innocuous oxidizing agent lvfor employment in accordancewith this invention.

While we have separately described 4the foregoing sulde treatmentycopper precipitation and iron precipitation, we have foundthatftheseste'ps are desirably combined to yield a', highly purified cobalt compound which, when subjected to electrolysis in` a customary electrolyte, yields a smooth, bright continuous cobalt deposit from strongly concentrated electrolytes not heretofore yielding a satisfactory deposit at elevated concentrations. For example, by first treating the cobalt solution with solution sulde in the presence of dissolved copper as above described, then EXAMPLE 1I Hydrogen sulphide gas was bubbled thru 9.97' liters impure CoSOi solution containing 1 g. added 5 CuSOi for one hour and twenty-five minutes. At the start the pH of the solution was 3.17, it was held between 2 and 3 by periodic additions of saturated soda ash solution. The sulphided solution was allowed to stand 1/2 hour and was separating the precipitate, then aerating the so- 10 then tereo by the use or filter ald- The filtrate lution in the presence of suitable quantity of dis- Was made lrlto a fluoborate electrolyte for Cobalt solved iron, again separating the precipitate, and eleetrowmnmg by adding 59 g/1- 331303 and 5 forming a cobalt electrolyte by the addition of a :ef-/l-rtarl' one trurd or thls s olutlon Wes used suitable quantity of boric acid and sodium fluoas 1S m the cobalt electrolytlo een' .The rst ride, we can secure very satisfactory electrode- Severt hour plate was fan" Another thrrd or the positions at concentrates as high as 30 grams per Sotutlon was treated as follows: The PH Was liter of dissolved cobalt or even at higher concentalsed to 5'95 Wlth soda' ash solution and then trations 5.27 g. FeSO4.7H2O were added. Finally, the so- The following examples show how the inventutton was warmed tot' 8 hours. between 6o qe' tion may be carried out but it is not limited greets- 70 degrees centlfade Wlth all bubblmg thereto. Parts and percentage compositions are thru 1t to Oxldlze the tron' It Stood overmght by weight unless otherwise designated, and the 331? Wsggrgvtrlle rrltlt gomg wigs? n tfhe a e as o aine or temperatures gwen are on the centlgrade Scale' this. The pH of the snai third of the e1ectro1yte EXAMPLE I was lowered to 3.01 by adding 3 cc. concentrated The cobalt was leached from 200 pounds stainsulphuric acid. Iron wire was then added to the ierite concentrates (CO2O3.H2O), 7.01 percent co- Solution, and air was bubbled through it for sevbalt, obtained from the Columbia Mine at Gooderal days- Finally, the iron was removed, the springs, Nevada, using 761/2 gallons 0f water, 27 solution oxidized, the pH adjusted to 6.0, and the pounds sulphuric acid and 39.7 pounds sulphur solution ltered ol. Upon electrolysis, an exceldioxide (to maximum efficiencyexcess Sulphur lent 1312368 0f Cobalt resulted. dioxide was used in the actual test). The solu- EXAMPLE In tlon was separated from the solids and measured 235 liters. The solution contained 97.4 percent TWO eltctrotytes were prepaired from the Som" of the cobalt in the concentrates. Residual comons rtuned m accordance Wlth Exemples I ano balt solutions relatively free of impurities and Itby mtotpotatmg 50 grams per rlter of bone obtained as by-products on experimental work amd and 5 grams per hter of ,Sodlum flu-onde, in the electrodeposition of cobalt were added to and thereafter the eonfentratlons of the two this solution to yield 278 liters of solution having electrolytes Were respectlvely adlusted to be .(a). the analysis of Table 1. To the head solution 20 grams per hter and (o) 39 grams Der hte? hydrogemsulphide was added under atmospheric of d1s solved cobalt. When subjected to electrolpressure (about '710 mm. mercury) in an interysrs m a sulteble eleotrolytle een employmg a mttent manner for about three days- The pH of sultable current density and a suitable voltage the solution was initially about 2.0 and this bethe fOuOWmg results Were Secured: came gradually more acid, the lowest pH being Table 2 pH time correlation 1.30. However, this was periodically raised by the addition of calcite to above pH 1.5 whenever Quality of Electroit fell below pH 1.4. In all, 7.0 pounds of hydropH Solution deposits from solutions gen sulphide were passed into the solution. The Test Tr'etttlnt cmtammg temperature of the solution was that found out of doors at Boulder City, Nevada, during the time Start End 2 gt Co 30 gft C0' of the treatment, and ranged from 10 degrees to 25 degrees centigrade. The hydrogen sulphide jjjjjjjjjj: gg gdood. precipitate weighed 161/2 pounds and had the 3 3.0 2.61 2.80 Good. analysis given in Table 1. The hydrogen sul- 4 3'0 4'22 ttt Excellent' phide precipitation was deemed complete when the standard colormetric test for copper failed Certaln temperature Correlations Were made to yield a positive test for this, equivalent to one Table 3 presents dalla Secured When a given head part per million. The solution was then further l sample 1S treated for three hOuIS at 2o Pounds treated for the removal of the iron and the recovper Square meh gauge hydrogen sulphide Dresery of the cobalt, sure in three tests, and the pH of the solution is determined. A combination of all of the Table 1.-Analyszs of solutions and products treated solutions yielded a good cobalt plate at 30 g./l. cobalt concentration, for '7 hours. Element Srgn Precipitatc Sion o5 Table 3.-pH temperature correlations Grams per Test l Initial pH l FinalpH Temp., C.

liter Per cent Cobalt 29. 2 5.1 Nickel 4.34 2. 52 21.4 Iron 4.34 1.92 20.5 Copper Nil. 4. 34 l. 78 15. 5 Manganese Magnesium climi... EXAMPLE IV Lead Negative. Bi, GdAS, S11 SbHg- Traces D0 Forty liters of impure cobalt sulphate electrolytes containing .1 gram per liter of copper sulaudace:-

7. phate and having an acidity of pH 1.5 is treated with hydrogen sulphide un'd'er a pressure of 20 pounds'persquare inch gauge -foron'e hour! *The solution was-filtered, and had-a pH 4r@1582. "2681 grams of precipitate were removed; l' The pI-Ioi thelsolution was then 'raised vto between-'5 and 6 by addition of soda-ash and 1.5' grams perl'liter of-copperas'was then added to fthe solution-.1 It

was then warmed to a 'temperature 'betw'eenf-GO'` degrees and 70 degrees centigradewhilea vigorous stream 'of air was passed through 'thelsol'u-4 tion and periodical additions of soda lash were' added to holdthe pH between 5 and 6. Afterl 24 hours, the fiocculent precipitate -was removed from thesolution, and at a cobalt concentration* of grams per vliter 'a good-plate of 'colcia'ltf was produced by electrolysis, thus indicating sub'staln# tial purification of the electrolyte.v

EXAMPLE V .A batch of cobalt electrolyteshavinga pH of 4.22 were sulphided by treatment with hydrogen` sulphide under a pressure of 20 :pounds-persquarc inch for three hours. At the end ro'f that time thek solutionV pH `was 3.56.- The mixture fof solution andwprecipitate was allowed to settlepand the solution was filtered with the 'aid of a suit-Y tated from the solution by the addition of satu rated soda ash solution and the precipitated c'o-` .balt carbonate was employed to inake a cobalt electrolyte that is to say, it `was dissolved `in sulphuric acid and suiiicient Water to make an aqueous solution containing 30 grams per liter of cobalt then 50 grams per liter of boric acid together with 5 gramsper literof sodiumv Vfluoride was incorporated inthe resulting solution. Upon electrolysis, van excellent cobalt plate, free from trees, nodules and the like was produced.

Various changes can be made in the invention as illustrated and described without departing from thespirit and scope thereof since many apparently widely differing 'embodiments will occur to onefskilled in the art.l

Whatis claimed is:

1. In a process for the production of a purifiedt The solution was then-treated by bub` cobaltsohitionsuitaible forcobaltfelectrowinning pur.poses,-thet "steps :whichl -comprise treating Aan impure 'cobaltf'solution containing at :least zinc as kan impurityfwit-h anfexcess of `hydrogen sulde under anfelevated-fpressure of atleast ten pounds persquare inch and at -a solution pH between pI-I 1an-d pH 6, whereby zinc is precipi tated as fa sulfide-and then separating-a -puriiied cobalt solution from the `resulting precipitate.

2. In-a process for-the .production of -a purified cobalt i solution sui-table for cobalt electrowinning purposesdrornan impure-cobalt salt .solution containingat Uleast foneJ impurity 'selected from the group consisting -ofA-zincpcadrnium, mercury,l arsenic, anti-mony, .gallium thallium, bismuth, pa1- ladium, .ruthenium osmium and indium, the steps whichwcomprise adjusting the solution .toV lie within the range pH 4 to pH 5, then adjustingv the `iron .and vcopper cmtent of the. .solution to lie within the range of 0.1 to lgramsper literl each-of iron .and-copper, treating-.the solution'- with an excess, .of hydrogen-sulfide under apres-- sure betweenabout Fl5 and. 10'() pounds lper square inch gauge, separating a precipitate containing copper suliide and other'inipurities, then adjusting? the solutionfpH l to lie between fpH 5 and -'pH 6, passi-ng atmospheric airA into and through. the resulting` solution wlrierebyy aviron 4and fother impur^ ities f are precipitated and A'remaining hydrogen sulfide stripped-off,` then removing.A and-discard ing-the` resulting precipitate to `yield a puried cobalt solution.'

VRUTH E. v-1CHlllRfC'I-IVSAILIRBD. FRANCIS SHEUIYON:f

CITED The following .references -farefof record jin ffitlie fue bf f-this patent:l

'UNTED STTE'SPTETS Number- Name Date1A 2,356,183 Shepard iet lal. inc e Aug. 22,y 1944 FOREIGN" PATEN TS' k@TH-'ER`v RFRENCES" Handbook :of Chemistry and Physics,.-16th edition, page 524:,4 f fChemicalfRubber'f Publishing Co.,-Cleve1and, Ohio ='(l931-)-. i 

